Page 189 - Chemistry ICSE Class X

Metallurgy 175
ƒ Storage. Alkali metals are stored (or kept) under kerosene or RCTCHſP
oil because they react rapidly with oxygen and moisture (present in
the air).
ƒ Metallic character. All alkali metals are strongly metallic (or highly
electropositive). Metallic (or electropositive) character increases as we
go down the group. Cesium is the most metallic element.
ƒ Ionisation energy. Alkali metals have low ionisation energy. The
ionisation energy decreases as we go down the group.
ƒ Electronegativity. Alkali metals have low electronegativity.
Electronegativity of alkali metals decreases down the group.
ƒ Reducing character. Alkali metals have strong tendency to lose
electrons. Thus, these metals act as strong reducing agents. Lithium is
the strongest reducing agent.
ƒ Oxidation state. Alkali metals exhibit only +1 oxidation state in their
compounds.
ƒ Nature of compounds. Alkali metals form electrovalent (or ionic)
compounds. However, some lithium salts have covalent character.
ƒ Flame colour. All alkali metals and their salts impart characteristic
EQNQWTU VQ C PQPNWOKPQWU ƀCOG CU FGUETKDGF DGNQY
Element: Li Na K Rb Cs
Flame colour: Crimson red Golden yellow Purple Violet Bluish
ƒ Extraction. All alkali metals are extracted by electrolytic reduction
method using molten hydroxides or chlorides.
ƒ Action of air. Alkali metals react with air or oxygen rapidly and get
tarnished due to the formation of oxide layer on the surface.
heat
4Li(s) + O (g) o 2Li O(s)
2
2
lithium from air lithium monoxide
heat
2Na(s) + O (g) o Na O (s)
2
2
2
sodium from air sodium peroxide
heat
M (= K, Rb, Cs) + O (g) o MO 2
2
superoxide
The oxides of alkali metals are basic in nature. With water, these oxides
give corresponding alkalis.
ƒ Action of water and acids. Alkali metals are highly electropositive.
These metals lose their only outermost electron very easily. This makes
alkali metals good reducing agents. It is due to this that alkali metals
displace hydrogen from compounds containing acidic hydrogen, viz.,
water, acids, etc. For example,
2Na(s) + 2H O(l) o 2NaOH(aq) + H (g)
2
2
sodium sodium hydroxide
Other alkali metals react in the same manner. The reaction becomes 'ƌŽƵƉ Ϯ
more and more vigorous in going from Li to Cs. Ğ
DŐ
Alkaline Earth Metals Ca

^ƌ
Elements of group 2 (or group IIA) are called alkaline earth metals.
Ă
Group 2 (or group IIA) contains, Beryllium (Be), Magnesium (Mg),
Calcium (Ca), Strontium (Sr), Barium (Ba) and Radium (Ra). These elements Ra
are collectively called alkaline earth metals because their oxides occur in the Alkaline earth metals occupy
earth crust and are alkaline in nature. Group 2 (or group IIA) of the
periodic table.